THE HEAD AND NECK 1 199 



Development. — The lateral nasal cartilages are derived from the cartilaginous 



core of the lateral nasal process. 



The cartilage of the septum is mesially placed, and is usually 

 inclined slightly to one side, most frequently the left. It forms a 

 large part of the nasal septum anteriorly, and has the form of an 

 irregularly four-sided, laterally-compressed plate. Its anterior 

 border is attached to the back of the nasal bones, along the course 

 of the intemasal suture; below this it is connected to the anterior 

 borders of the upper lateral nasal cartilages ; and below these it lies 

 between the middle crura of the lower nasal cartilages. Its pos- 

 terior border is accurately applied to the irregular anterior margin 

 of the perpendicular plate of the ethmoid bone. Its inferior border 

 is received into the front part of the groove on the anterior border 

 of the vomer. The antero-inferior border passes upwards and for- 

 wards from the front part of the inferior border to the anterior 

 border. In early life the septal cartilage is prolonged backwards to 

 the body of the sphenoid bone in the form of a narrow strip, which 

 intervenes. between the lower border of the perpendicular plate of 

 the ethmoid and the vomerine groove. This portion is known as 

 the sphenoidal or posterior process. Along the inferior border of the 

 septal cartilage, between it and the anterior border of the vomer, 

 there are two narrow, elongated strips of cartilage, right and left, 

 which are called the cartilages of Jacobson, or the vomerine car- 

 tilages of Buschke. 



Development. — The septal cartilage is derived from the chondrocranium. 



The Temporal and Ptergyo-maxillary Regions. 



Muscles of Mastication. — ^These are four in number, namely, the 

 masseter, temporal, external pterygoid, and internal pterygoid. 



Masseter — Origin — (i) Superficial Portion. — The anterior two- 

 thirds of the lower border of the zygomatic arch. (2) Deep Portion. 

 — ^The posterior third of the lower border, and the whole of the 

 deep or internal surface of the zygomatic arch. 



Insertion. — ^The superficial portion is inserted into the lower half, 

 and the deep portion into the upper half, of the outer surface of the 

 ramus of the inferior maxilla. The superficial fibres extend as far 

 as the angle, and the deep fibres encroach on the coronoid process. 



Nerve-supply. — ^The masseteric branch of the anterior portion of 

 the inferior maxillary division of the fifth cranial nerve. This 

 branch emerges from the pterygoid region by passing over the 

 sigmoid notch of the inferior maxilla, below the zygoma, and it 

 therefore enters the muscle on its deep surface, accompanied by 

 the masseteric artery. 



The superficial portion of the muscle is directed downwards and 

 slightly backwards, and the deep portion downwards and very 

 slightly forwards. 



