48 



BONES OF THE HEAD. 



ethmoid and sphenoid as far as the frontal bone. This condition^ results from the 

 union with the palate bone of a separate centre of ossification, more usually united 

 with the ethmoid or sphenoid, and already described with the sphenoidal spongy 

 bone (p. 40). 



The sphenoidal process curves upwards, inwards, and backwards from the 

 posterior part of the vertical plate. Its superior or external surface is in con- 

 tact with the sphenoidal spongy bone and the base of the internal pterygoid 

 plate, and is grooved for the completion of the ptery go-palatine canal ; its 

 internal or under surface looks to the posterior nares ; and at its base a third 

 surface looks forwards and outwards into the spheno-maxillary fossa. Its 

 inner extremity is in contact with the wing of the vomer. 



The spheno-palatine foramen is formed in greatest part by the deep notch 

 between the orbital and sphenoidal processes, and is completed above by the 

 sphenoidal spongy bone. It leads from the spheno-maxillary fossa into the 

 nasal cavity, and transmits the internal nerves from Meckel's ganglion and 

 the nasal branch of the internal maxillary artery. 



THE VOMER. 



The vomer is a thin mesial bone, irregularly quadrilateral, and placed 

 vertically between the nasal fosss6. It articulates with the sphenoid, eth- 

 moid, palate, and maxillary bones, and with the septal cartilage of the nose. 

 As it usually becomes united by anchylosis, at an early age, to other 

 bones, and is frequently more or less absorbed and even distorted in some 

 of its parts, it can be best studied as a separate bone in young specimens. 



Fig, 41. 



Fig. 41. THE VOMER. | 

 A, from the right side ; B, from above. 

 1 ] ', the upper everted edges, or alse, on each 

 side of the hollow -which receives the rostrum 

 of the sphenoid; 2, the anterior or ethmoid 

 border, grooved to receive the septal cartilage 

 of the nose, and prolonged at x into a process 

 which rests upon the nasal crest ; 3, the pos- 

 terior or free border ; 4, the inferior or 

 maxillary and palatine border, 



The part of the vomer which lies below the diagonal line 

 extending from its posterior to its anterior extremity is a 

 thin mesial plate, that which lies above this line consists of 

 two alee,, rising on each side of a mesial groove, in which lies 

 the septal cartilage of the nose. The alee posteriorly are 

 thick and expanded, and form the bifid posterior extremity of 

 the bone, which rests beneath the sphenoid. The superior 

 border of each ala, extending forwards from that point, arti- 

 culates edge to edge with the lamella projecting at the base 

 of the internal pterygoid plate, the sphenoidal process of the 

 palate bone, and the extremity of the rostrum of the sphe- 

 noid ; the anterior border, sloping downwards and forwards, 

 in contact with the septal cartilage, is free in the inferior part, 

 and is united superiorly by anchylosis on one or both sides with the 

 central plate of the ethmoid. The anterior extremity of the vomer forms 

 a short vertical line which fits in behind the nasal crest of the maxillaries, 

 and from the upper end of which a process projects forwards in the groove 



