572 CLASS XVII. 



the zygomatic process of tlie temporal bone wliicli is united to the 

 superior maxillary. The palate-bones, which are placed between 

 the superior maxillary bones and the pterygoid processes of the 

 sphenoid, have in most mammals a longer horizontal piece, by 

 which the posterior part of the hard palate is formed. That this is 

 imperfectly ossified in the marsupial animals and that thus the bony 

 palate in their heads presents larger or smaller apertures, is one of 

 the osteological characters by which Owen distinguishes this divi- 

 sion of mammals. The pterygoid bones [pterygo'ide interne of 

 reptiles Cuv., the outer plate of the pterygoid process of the sphe- 

 noid in man) continue long distinct from the sphenoid, and in some 

 mammals permanently soi. 



The lower jaw differs by two characters from that of the other 

 vertebrate animals; first by its condyle being received by an arti- 

 cular cavity of the temporal bone; next, by its articular portion 



^ [Having given the formation of the bodies and neural arches of the cranial 

 vertebrae from Owen's great work, we subjoin that of the inverted haemal arches in the 

 mammals : 



In the occipital vertebra: the haemal arch is represented in many mammals by the 

 pleura-pophysial element only, the scapula; in many there is a haemapophysis, the 

 coracoid, which coalesces with the pleurapophysis, and which completes the arch in 

 the monotremes alone by joining the episternal. In many mammals again the arch is 

 completed by bones whicli appear to be haemapophyses of the atlas, the clavicles. The 

 diverging appendage of the occipital inverted arch is the anterior limb. 



In the parietal vertebra : the arch consists of pleurapophysis, the styloid, united to 

 haemapophysis, the lesser cornu of hyoid, by ligament and haemal spine, the body of the 

 hyo'id. The diverging appendage is the posterior cornu of the hyoid, the thyrohyal. 



In the frontal vertebra: the pleurapophysis is the tympanic bone, the hffimapophy- 

 sis the lower jaw or mandible, the hasmal spine the symphysis. There is no diverging 

 appendage of this vertebra in any vei-tebrate class above that of fishes, in which it is 

 formed by the opercular bones. Note that in this inverted arch the pleurapophysis is 

 separated from its haemapophysis by the intrusion of the diverging appendage of the 

 next vertebra, which thus in mammals receives the condyle of the lower jaw, assuming 

 here the office performed by the tympanic in the other vertebrate classes. 



In the nasal vertebra the pleurapophysis is the palate-bone, the haemapophysis the 

 supei-ior maxillary, the haemal spine the two praemaxillaries. Here the diverging 

 appendage consists of a bone which connects this vertebra with the descending process 

 of the sphenoid, and with which process it usually coalesces, forming the outer lamina 

 of the pterygoid process : and further of two other elements, succeeding each other, of 

 which the proximal piece is the malar, the distal the squamosal which expands as it 

 diverges. Owen Homol. p. 132. 



Hence, exclusive of the olfactory capsule and the muco-dermal bones, the lachrymal 

 and turbinate, the bones of the face in mammals all belong to the inverted arches of 

 the nasal and frontal vertebrae.] 



