## 1 Introduction  
### Nasal Septal Growth and Facial Development  
The growth and development of the nasal septum and the processes by which it influences other facial structures is a topic highly debated by scientists and still poorly understood, with some authors claiming that nasal septal growth continues well into adulthood (for a review of studies of nasal septal measurements, see [1]). In this context, a theory, called Functional Matrix theory, was introduced by [PERSON] in 1968 [2]. It postulated that the cranium is made up of multiple functional and skeletal matrices. A functional matrix is defined as \"non-skeletal cells, tissues, organs, and operational volumes\" present in the body, while skeletal matrices form around the functional matrices as protection and support [2]. These functional matrices can be represented by organs,muscles, a volume, or a space that have a specific craniofacial function. Skeletal matrices develop in support of the adjacent functional matrices and can be described as \"bone, cartilage, or tendons tissues\" [3]. One of these functional matrices is the nasal cavity. [PERSON] believes that the nasal cavity is structurally supported by the skeletal matrix of nasal septum, whose only role is to act as a pillar to support the roof of the nasal cavity. Due to its role, according to [PERSON], the nasal septum grows as a secondary response to the primary growth of the functional matrices of the face, particularly the nasal cavity, as well as facial muscles and other functional matrices of the face, such as the orbits [4]. This interpretation is in opposition to another well-received theory by [PERSON]. [PERSON]'s theory hypothesises that cranial development is encouraged and influenced by cartilage expansion centres, one of these being the nasal septal cartilage [5]. [PERSON] suggests that, as carilaginous areas grow, this causes the growth, development, and displacement of adjacent facial features. He states that, as the nasal septum cartilage grows, it causes the facial bones, not including the mandible, to be thrust downwards and forwards and to separate. In contrast to [PERSON]'s theory, [PERSON] states that during the first phase of facial development, growth is \"regulated by the cartilage of the nasal septum, cranial base and mandibular condyle\", and these carilaginous structures act as pacemakers for the early growth of the facial skeleton [5]. Research has continued to test these theories and to investigate the influence of the nasal septum on human facial development. A longitudinal twin study was carried out in 1997, where one of the twins suffered a nasal septal destruction and reconstruction (with cartilage implantation) at age 7 [6]. When measurements of the twins were compared at age 17, there were clear differences in maxillary growth and development, with the affected twin having a growth disturbance leading to a smaller maxilla vertically and horizontally. These findings seem to suggest an influence of the nasal septum on the growth and morphology of the facial bones, particularly the maxilla, thus supporting [PERSON]'s interpretation of the nasal septum as a pacemaker for facial growth. More recently, [PERSON] et al. [7] \"assessed the morphological relationship between nasal septal deviation and asymmetries of the facial skeleton in adults\". Their results showed a significant relationship between nasal septum deviation and asymmetry of the nasal and palatal regions in adults. However, no asymmetry in more lateral regions of the face was found. In contrast, other studies revealed findings in support of [PERSON]'s theory of the septum which is a secondary structural aspect of facial development [8; 9; 10]. These studies suggest that the septum has a passive role and is subject to change by neighbouring skeletal structures, proposing that nasal septum deviation is dependent and constricted by other aspects of the nasofacial region elements. In a recent study, nasal septal deviation has been linked to a reduction in the height of the upper facial skeleton [11].