DORSAL ASPECT OF THE SKULL. 181 



505. I., Infundibulum. This is the opening from the frontal sinus to the nasal 

 cavity. 



506. M. a. i., Meatus auditorius internus Internal auditory meatus. This is 

 divided into two parts very near its mouth, as shown by the white line. The ventral part 

 receives the auditory nerve (VIII), the dorsal part, the facial (VII). The facial in its course 

 curves round in the dorso-lateral part of the Pars petrosa and finally emerges at the stylo 

 mastoid foramen. This passage through the skull from the M. a. i. to the stylo-mastoid 

 foramen is known as the Aquaeductus Fallopii. In the Pars petrosa, about 2 mm. from 

 its mouth, there branches cephalad a small canal, the Hiatus Fallopii, which opens oppo- 

 site the ventral end of the osseous tentorium. 



507. O. soc., Os supraoccipitale, az. Supraoccipital bone. This forms the caudal 

 part of the roof of the cranial cavity. 



503. O. i. p., Os interparietale, az. Interparietal bone. A small bone, separate in 

 young animals. It is cephalad of the Supraoccipital and is wedged in between the caudal 

 ends of the parietals. 



509. O. parietale Parietal bone. The parietal bone forms a large part of the side 

 and roof of the cranial cavity. 



510. O. perioticum *. petrosum. This is a part of the temporal bone ; it encloses 

 the internal ear, and is divided into two parts, Pars petrosa and Pars mastoidea, the latter 

 appearing on the ectal surface of the skull (Fig. 57). 



511. O. temporale Temporal bone. This forms part of the floor and side of the 

 cranium, and by its zygomatic process helps to enclose the temporal fossa. 



512. O. boc., Os basioccipitale, az. Basioccipital bone. It forms part of the floor 

 of the cranium. 



513. O. bsph., Os basisphenoideum, az. It forms the caudal part of the body of 

 the sphenoid bone, and helps to make the floor of the cranial cavity. 



514 O. alsph., Os alisphenoideum, This is one of the greater wings of the sphe- 

 noid and forms part of the side and floor of the cranium. 



515. O. orsph., Os orbito-sphenoideum. This is one of the lesser wings of the 

 sphenoid ; it forms part of the floor and side of the cranium and part of the mesal wall 

 of the orbit. 



516. O. frontis The frontal bone. The frontal bone forms a large part of the roof 

 and part of the side of the cephalic region of the cranial cavity and the mesal wall of the 

 orbit. It also covers the caudal part of the nasal cavity. 



517. O. pit., Os palatinum Palate bone. This is a very complex bone, forming, 

 part of the orbit, of the roof of the mouth, and of the floor and side of the nasal cavity. 



518. O. malare s. Os zygomaticum, os jugale Malar, zygomatic or jugal bone. 

 This bone connects the malar and zygomatic processes of the maxilla and the temporale, and 

 with them encloses laterally the orbit and the temporal fossa, and completes the Zygoma 

 or zygomatic arch. 



519. O. pin., Os planum. This is not a separate bone, but merely the orbital part 

 of the ethmo-turbinal. It is often absent. 



520. O. Ich., Os lachrymale Lachrymal bone. It is a thin quadrilateral bone 

 forming part of the cephalic wall of the orbit and the caudal part of the nasal cavity. 



521. O. maxillare Maxilla, superior maxillary or upper jaw bone. This is a com- 

 plex bone which forms a great part of the face. In it are implanted the dorsal (upper) 

 molar, praemolar and canine teeth. 



522. O. nasale Nasal bone. A thin irregular bone forming part of the roof of the 

 nasal cavity. 



