n8 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



tube. The meatus leads into the cavity of the bulla, which is the tympanic cavity 

 or cavity of the middle ear. From the dorsal side of the bulla a ridge begins 

 which proceeds across the posterior part of the skull to the other bulla; this 

 ridge is the superior nuchal line (or lambdoidal ridge) and is the most anterior 

 point of attachment of the muscles of the vertebral column. From the middle 

 of this ridge there projects posteriorly the external occipital protuberance, slight 

 in the cat but forming a rectangular prominence in the rabbit. 



On the ventral surface the anterior part of the skull is occupied by the hard 

 palate. Dorsal to this are the nasal passages which open at the posterior end of 

 the hard palate by the posterior nares or choanae. The hard palate contains a 

 pair of openings, the incisive foramina or anterior palatine foramina; these are 

 small and at the anterior extremity of the palate in the cat but much longer and 

 more prominent in the rabbit. They lead into the nasal cavities. At the 

 posterior end of the zygomatic arch on its ventral side is a depression, the man- 

 dibular fossa, for the reception of the lower jaw. Medial to this is the pterygoid 

 fossa for the attachment of certain muscles. The pterygoid fossa in the cat is 

 continuous with the temporal and orbital fossae, while in the rabbit it is included 

 between two projecting plates of bone which point toward the tympanic bulla. 



2. Membrane bones of the roof of the skull. — Beginning just behind the 

 anterior nares are the paired nasals, roofing the nasal cavities; next posterior, 

 the paired frontals; and last, the paired parietals, terminating at the superior 

 nuchal line. Between the posterior ends of the parietals is generally a small 

 triangular interparietal bone, the boundaries of which are not always distinct. 

 Each frontal bone forms the dorsal part of the orbit and projects out above the 

 orbit as the supraorbital arch which terminates posteriorly in the zygomatic 

 process of the frontal bone, already noted. In the anterior wall of the orbit is 

 the small lacrimal bone (probably homologous with the prefrontal bone of 

 reptiles). At the anterior end of the lacrimal bone is an opening, the posterior 

 end of the nasolacrimal duct, by means of which the tears drain into the nasal 

 cavity. 



3. The bones of the upper jaw. — These as in the alligator comprise a lateral 

 maxillary arch on each side and a median series of bones. The maxillary arch 

 consists on each side of the following elements: premaxilla, in front of the 

 anterior nares and bearing teeth; maxilla, forming the side of the facial region 

 of the skull and also bearing teeth; malar or jugal, forming most of the zygomatic 

 arch; and temporal, completing the zygomatic arch and covering the side of the 

 cranial part of the skull including the tympanic bulla. Further details concern- 

 ing these bones may be noted. The premaxillae send frontal processes dorsally 

 alongside the nasal bones; these are very pronounced in the rabbit. The pre- 

 maxillae also form the anterior part of the hard palate by means of their palatine 

 processes, which meet in the median ventral line and include the incisive foramina. 

 The maxilla is the main bone of the facial region; in the rabbit it is much fenes- 



