INTRODUCTION
The name of Ayukawa is well known in Japan, as a place, where many whales of large and small size are landed and treated. On August 26th, 1958, a small strange whale was seen in a whaling company at Ayukawa. Only one pair of square topped teeth was found at the middle of the lower jaw. The teeth were very wide and flat, so the upper jaw was This news was brought to Mr. Yoshinori Kimura, who is narrowed. a strenuous co-operator in our research group on whales, and soon he went to the whaling company for the purpose of observing the object. He arrived at the whaling company, however, after the dissection had been finished. He could neither examine nor take photograph of the whale ; so, he collected as much as possible the remains of the whale body. Fortunately the almost complete skeleton remained. It was buried in the sand of the Kugunari beach. At that time, the gunner of that catcher boat wished to have the curious teeth for souvenir. Mr. Y. Kimura had a tooth of the same species which had been collected in there bone-yard, so he asked the gunner to exchange it with the newly taken teeth and it was agreed. Considering the situation above mentioned, this is not the first time of It is presumable that this species might be the catch of this species. taken by the whalers for Ziphius cavirostris, which is not a rare whale in Japan. About three months later, the senior author visited the whaling station of  Ayukawa  with  Dr. H. Omura, Messrs. T. Ichihara and K. Nasu of the  Whales  Research  Institute and  exhumed  the  buried   remains   with The skeleton had been macerated to the perfection Mr. Y. Kimura. and it was transported to the Whales Research Institute of Tokyo for The whale in question was captured on August 25th, further study. by a catcher boat, about 65 miles SE off Ayukawa (37°27′ N. 142°30′ E.). It was a male and measured about 5.3 m, in length, has black coloured skin on the whole body except on the jaws. Mesoplodon had hitherto been reported from many districts of the * Department of Anatomy, Faculty of Medicine, University of Tokyo. In Japan, there have been two precedents, one was reported by world. Professor T. Ogawa (1938) and the other was reported by us last year. Therefore, this specimen seems to be the third one so far as scientifi- cally reported, and represents perhaps the most southern catch of M. stejnegeri in the world. The authors should like to thank to Mr. Yoshinori Kimura and to the personnels of the Whales Museum of Ayukawa for their kindness in al- lowing us to have the opportunity of studying this precious material. The authors are much indebted also to Professor T. Ogawa, Director of the anatomical department of Tokyo University for his guidance and to Dr. H. Omura and his staff Messrs. T. Ichihara and K. Nasu for their collaboration in examination of the skeleton. The external appearance of this specimen is very poorly known, only several sheets of photographs were taken by Mr. Tokinori Watanabe of Nippon Medical College. These photographs are concerned to about the So it is head part only, but are serviced as coloured transparencies. shown as colour print in the Plate I, because seeing is better than reading. Measurements of the present specimen are shown in Table 1 and Skull. the two skull measurements from precedent reports are shown in Table 2 for the purpose of comparison. The photographs of the skull in lateral, dorsal and ventral views are shown Plate II. The most noticeable character of the skull is that the peculiar shaped large teeth are seen vertebral column, C7 + D11 + L9 + Ca19=46 at the mandible behind the symphysis and the lateral basirostral grooves are clearly present. Vertebrae. The total number of the vertebrae amounts to 46, with the formula of C: 7, D: 11, L: 9, Ca: 19. The first and second cervical vertebrae are ankylosed together at the bodies as well as at the neural arches. The vertebral bones show some deficit ; namely the transverse processes of the 7th cervical vertebra, the 11th dorsal vertebra and the spinous processes of the 5th and 6th lumbar vertebrae are missing. Unfor- tunately, 17th caudal vertebrae was bitten by a dog. We have to apologize for the latter accident. The first caudal vertebra is determined by existence of the first chevron. The first chevron was found only in the left joint region, because the other parts of it was cutted off at the dissection. All the chevrons are 9 in number and were collected except the second chevron. In all the vertebrae the epiphyses are fused to the diaphyses, which tells evidently the physical maturity of the present specimen. Ribs. The ribs were collected in perfection. They are shown in Fig. 3 Two headed ribs are seven, the eighth and nineth are and Table 6. lengthened but the most posterior two ribs are very shortened. Pectoral limb. _ The scapulae are nearly symmetrically fan-shaped as in other species of Mesoplodon. The humerus, radius and ulna are not conspicuously different from the correspondent bones in other species of Mesoplodon and the proximal and distal epiphyses of those bones are all ankylosed. The phalangeal formula including the metacarpals is as follows; I:1, II:5, III:5, IV:4, V:3. This formula is equal on both The authors suggested at that occasion that it is necessary sides. to take the Röntogen photographs for studying the bones of the pecto- ral limbs in fresh condition, but in reality Röntogen photograph of the present specimen was not taken. Measurements of the bones of the pectoral limb are given in Tables
TABLE 1. SKULL DIMENSIONS OF THE AYUKAWA SPECIMEN
TABLE 1. SKULL DIMENSIONS OF THE AYUKAWA SPECIMEN (Cont.)
The skull is much worn around the left notch and the measurements is only 3) approximate,
(mm)
TABLE 5.  DIMENSIONS OF THE VERTEBRAE (mm)
reatest height of Gr 41 41 39 42 48 46 48 52 55 60 60
car of neural o 55 54 50 44 41 42 45 45 50 48 51 48 46 40 38 31 29 29 28 28 27 28 28 18 20 18 14 11 13 10 11 8 7 7 6 6 w 2 | l ー ( --- l | - 3 and 4 and the photographs are shown in Fig. 2. But Sternum and Hyoid bone. The sternum consists of four segments. the third and fourth one was ankylosed conjointly. Dimension of several parts are shown in Table 7. Photograph and some dimensions of the hyoid bone are shown in Fig. 5 and Table 8. The basihyal and thyrohyals are ankylosed loosely.
1) Not given, for it is broken. 2) Missed.
TABLE 7.  DIMENSIONS OF THE RIBS  (mm) 1) Along the vertebral border 2) It has some deficit
TABLE 9. DIMENSIONS OF BASIHYAL, THYROHYALS AND STYLOHYALS (mm)
45 Bone of pelvic region. It was collected on one side only, and it is dif- ficult to decide which side it belonged to and which end of the bone is the anterior. Its photograph is shown in Fig. 8. Addendum. The salivary gland of this whale is being studied at Depart- ment of Pathology, Nippon Medical College. As shown in the precedent report of the authors (1958), four distinc- tive characters are especially to consider in classifying the species of Mesoplodon. The first is the relative position of the premaxillary and maxillary foramina. In the present specimen the premaxillary foramina are situated in the same level or slightly caudal to the maxillary fora- mina. The second is the presence or absence of the lateral basirostral groove, and this groove is clearly found in the present specimen (Fig. 9). The third is the position, where the teeth are situated in the mandible. In the present specimen the teeth are situated at the caudal end of the symphysis, The fourth character is the shape of the teeth, especially the ratio between the transverse thickness and the antero-posterior breadth at the place of insertion into the mandibular alveole. This important key for classifying the species more in ratio gives an The teeth are large flat and square topped in the present speci- details. The ratio of thickness to antero-posterior breadth of the teeth men. is 1:6.5 on the left tooth, 1:6.4 on the right tooth. This ratio is higher than in any other Mesoplodon species. From the above mentioned results applying the keys upon the species of Mesoplodon reported by Raven (1937) and by the authors (1958), the present specimen might be classified as  Mesoplodon stejnegeri. An adult male beaked whale that belongs to the genus Mesoplodon was captured on August 25th, 1958, off Ayukawa in Japan. The external characters of the whale body could not be observed, but the skeleton was almost perfectly collected and is preserved in the Whales Museum of Ayukawa. From the osteological examination the present specimen may sufficiently be classified as Mesoplodon stejnegeri. Hubbs, C. L. (1946). First records of two Beaked whales Mesoplodon bowdoini and Ziphius cavirostris, from the Pacific coast of the United States. J. Mammal., 27 (3): 242-55. Nishiwaki, M. & Kamiya, T. (1958). A beaked whale Mesoplodon stranded at Oiso beach, Japan. Sci. Rep. Whales Res. Inst., no. 13: 53-83.
Norman, J. & Fraser, F. C. (1937).  Giants Fish, Whales and Dolphins.  London, Putnam. Orr, R. T. (1953).  Beaked whale (Mesoplodon) from California, with  comments  on  taxo- nomy.  J. Mammal., 34 (2): 239-49. R AVEN , H. C. (1937). Notes on the taxonomy and osteology of two species of Mesoplodon (M. europaeus Gervais, M. mirus True). Amer. Mus. Nov., 905: 1-30. - True, F. W. (1910). An account of the beaked whale of the family Ziphiidae etc. Bull. U. S. Nat. Mus., 73: 18. VAN BENEDEN, P. S. & DAUL, G. (1880). Ostéographic des Cétacés, vivants et fossiles. Paris, Arthus Bertrand, 1: 1-634. Fig. 1. Lateral view of head of Mesoplodon stejnegeri from Ayukawa, showing its body colour. Lateral view of skull of Mesoplodon stejnegeri from Ayukawa, mandible in oc¬ Fig. 2. clusion. Fig. 3. Anterior view of skull of Mesoplodon stejnegeri from Ayukawa, mandible in oc¬ clusion. Posterior view of skull of Mesoplodon stejnegeri from Ayukawa. Fig. 4. PLATE II Lateral, dorsal and ventral views (top to bottom) of skull of Mesoplodon stejnegeri from Ayukawa. Lateral, dorsal and reversed lateral views (top to bottom) of mandible of Mesoplodon stejnegeri from Ayukawa. PLATE IV Fig. 1 and 2. Lateral and caudal views of cervical vertebrae of Mesoplodon stejnegeri from Ayukawa. Fig. 3 and 4. Cranial and caudal views of each cervical vertebrae of Mesoplodon stejnegeri from Ayukawa; from left to right, 1~2, 3, 4, 5, 6, 7th of cervicals. Fig. 5. Lateral view of skeleton of Mesoplodon stejnegeri from Ayukawa, which was set uped by Mr. Y. Kimura. M. NISHIWAKI AND T. KAMIYA