COMPARATIVE ANATOMY 19 



remains as a core within each ramus. What has become of the 

 gill arches in the reptiles ? 



Skull of the Cat 



In the cat, as in all mammals, bone has replaced cartilage 

 almost entirely, at least in adults. There is also a tendency 

 for bones to unite with one another so that the mammalian 

 skull contains fewer bones than a similar skull of its amphibian 

 or reptilian ancestors. The following features serve as 

 landmarks: 



Orbits (eye sockets). — Are they completely surrounded by 

 bone } Compare with the skulls of other mammals in this 

 respect. 



Temporal fossa (fossa, ditch), a space just behind the orbit 

 into which a projection from the lower jaw extends. 



Zygomatic arch (zyge, yoke), the bar of bone ventral to the 

 orbit and temporal fossa. 



Foramen magnum, the large hole at the posterior end of the 

 skull through which the spinal cord passes to the brain. 



Occipital condyles, bony projections on either side of the 

 foramen magnum for the articulation of the skull with the 

 first vertebra. 



Nares, the nostrils. 



Lambdoidal ridge (from Lambda, the Greek letter L), an 

 arched ridge of bone extending transversely dorsal to the fora- 

 men magnum. 



Sagittal crest (sagitta, arrow), a ridge extending anteriorly 

 from the center of the lambdoidal ridge. Both the lambdoidal 

 ridge and the sagittal crest are Inconspicuous or absent in kitten 

 skulls. 



Tympanic bullae (bulla, bubble), paired swellings on the 

 ventral side of the skull, anterior to the occipital condyles. 

 Each contains the bones and sensory part of the ear. 



External auditory meatus (meatus, passage), the opening on 

 the lateral side of each tympanic bulla. 



Choanae (choana, funnel), posterior openings of the nasal 

 passages on the ventral side of the skull. 



The bones of the skull will be described In order, as far as 

 possible, beginning at the posterior end. Each bone should be 



