156 



SKELETON OF THE DOG 



is a narroAv pointed nasal part which fits in between the nasal bone and the maxilla. 

 The orbital and temporal parts are relatively extensive. Two ethmoidal foramina 

 are commonly present. The frontal sinus is confined to the frontal bone. 



The parts of the temporal bone fuse early. The zygomatic process curves 

 widely outward and forward. Its anterior part is beveled below and articulates 

 extensively with the corresponding process of the malar. The articular surface 

 for the condyle of the mandible consists of a transverse groove which is continued 

 upon the front of the large postglenoid process. Behind the latter is the lower 

 opening of the parieto-temporal canal. There is no condyle. The mastoid part 

 is small, but bears a distinct mastoid process. The external auditory meatus is 

 large and the canal very short, so that one can see into the tympanum in the dry 

 skull. The bulla ossea is very large and is rounded and smooth; the inner side 

 is united to the basioccipital. Above this junction and roofed in by the union 



of the petrous part and the basi- 

 / occipital is the petro-basilar 



canal (Canalis petrobasilaris) ; 

 this transmits a vein from the 

 floor of the cranium to the 

 foramen lacerum posterius. 

 The latter is in reality a de- 

 pression and is situated behind 

 the bulla ossea. In its pos- 

 terior part is a foramen which 

 transmits the ninth, tenth, and 

 eleventh cranial nerves. The 

 carotid canal branches off from 

 the petrobasilar, passes forward 

 external to it through the inner 

 part of the bulla ossea, and 

 opens in front at the carotid 

 foramen; it transmits the in- 

 ternal carotid artery. The Eu- 

 stachian opening is immedi- 

 ately external to the carotid 

 foramen. The muscular and 

 hyoid processes are extremely 

 rudimentary. The petrous part 

 projects into the cranial cavity 

 and forms a sharp prominent 

 petrosal crest. The inner sur- 

 face presents a deep floccular 

 fossa alcove the internal auditory meatus. The anterior surface is also free. 

 The anterior angle is perforated by a canal for the fifth cranial nerve (Canalis 

 nervi trigemini). 



The body of the sphenoid bone is flattened dorso-ventrally. The sella turcica 

 is shallow, but the dorsum selUp is well developed and bears posterior clinoid 

 processes. A pair of anterior clinoid processes project back from the roots of the 

 orbital wings. The latter are relatively small and are crossed externally by a 

 crest, which is continued forward upon the palate bone. The temporal wings are 

 extensive and articulate above with the parietals. Perforating the roots of the 

 wings are the following foramina, named from before backward: The optic passes 

 through the orbital wing. The foramen lacerum orbitale is a little lower and is 

 at the junction of the wings. The foramen rotundum opens into the alar canal, 

 which passes through the root of the short but wide pterygoid process. The 



Fig. 124. — Cranial Cavity of Dog. as Seen on Sagittal Sec- 

 tion OF Skull. 

 /, Roof of cranium; //, base of cranium; ///, posterior wall 

 of cranium; IV, anterior wall of cranium; A, anterior cranial fossa; 

 B, middle cranial fossa; C, posterior cranial fossa; a, body of pre- 

 sphenoid; a', body of postsphenoid; c, palate bone; d, vomer; e, 

 occipital; /, occipital condyle; g, sagittal crest; h, frontal sinus; 

 h', cranial plate of frontal bone; i, cribriform plate of ethmoid bone; 

 i', ethmoidal foramen; k, ethmoturbinals; I, parietal bone; l', I", 

 squamous temporal bone; I'", temporal wing of sphenoid bone; 

 m, sella turcica; m' , ilorsum sella; n, optic foramen; o, foramen 

 lacerum orbitale; p, foramen rotundum; q, foramen ovale; r, ?•', 

 carotid foramina; s, tentorium osseum; t, foramen lacerum; u, u' , 

 orifices of parieto-temporal canal; i% condyloid canal; w, canal for 

 trigeminal nerve; x, internal auditory meatus; y, y' , orifices of canal 

 for inferior occipital sinus; z, floccular fossa. (After Ellenberger, 

 in Leisering's Atlas.) 



