STERNUM AND SKULL. 



295 



lage-bones, membrane-bones are largely developed; and the 

 two groups of bones, though primitively distinct, become in- 

 timately and immovably united to form a complex structure, in 

 which the several morphological components, and even the 

 boundaries of individual bones, are difficult to determine, and 

 of which the essential composition can only be ascertained 

 by a study of the embryonic stages. 



In the following description the membrane-bones are 

 described in connection with the cartilage-bones with which 

 they are most closely associated, and their names are printed 

 in italics. Though it is convenient to deal with the membrane- 



F.M. B.O. B.S. PtA. 



Fig. 59. — Lepus ouniculus. The skull from the right side. The middle 

 portion of the zygomatic arch and the right half of the mandible 

 have been removed, (a, m. m.) 



A. external pterygoid process of ali-sphenoid. AS, ali-spUenoid. B, in 

 ternal orbital foramen. BO, basi-occipital. BS, basi-sphenoid. Cf, occipital 

 condyle. D, mandibular symphysis. EO, ex-occipital. F, frontal. jPA, 

 foramen laceritm anterius. FM, foramen ovale, confluent with the foramen 

 lacerum medium. Gr, orbital groove, for ophthalmic division of trigeminal 

 nerve. I, anterior upper incisor. IF, infraorbital foramen. IP, inter- 

 parietal. J, lower incisor^ Xi, lacrymal bone. LF, lacrymal foramen. M, 

 maxilla. MI3", mandibla K", nasal bone. OF, optic foramen. OS, orbito* 

 sphenoid. P, parietal. PE, par-occipital process of ex-occipital. PL, pala- 

 tine bone. PM, pre-maxilla. PO, periotic. PT, pterygoid. S, squamosal- 

 SF, stylo-mastoid foramen. SO, supra-occipital. T, tympanic bones. ZM, 

 zygomatic process of maxilla, cut short. ZS, zygomatic process of squamosal, 

 ant short". 



