no LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



with the parietal. In front of the dorsal portion of the opisthotic is an area 

 of cartilage, and in front of this is the prootic bone. Extending from the opisth- 

 otic obliquely forward and laterally is a slender membrane bone, the squamosal. 

 The posterior part of the squamosal covers a part of the opisthotic and lies 

 above the lateral border of the otic capsule. The prootic bone is wedged in 

 between the squamosal and the parietal. On turning the skull laterally so as 

 to obtain a lateral view of the otic capsule a small rounded bone will be found 

 situated in the lateral wall of the otic capsule. It articulates behind with the 

 opisthotic and bears a dorsally projecting process which meets a ventrally directed 

 process from the middle of the squamosal. This rounded bone is called the 

 columella and is believed to be equivalent to the hyomandibular bone of fishes, 

 that is, the dorsal portion of the hyoid gill arch. The internal ear is located 

 inside of the prootic bone, and the columella fits into an opening in the prootic 

 bone, called the. oval window or fenestra ovalis. The columella, when the middle 

 ear appears (first in Anura), becomes a bone of the middle ear, and it, or at 

 least that portion of it which fits into the fenestra ovalis, is probably homologous 

 with the stapes of the mammalian middle ear. The homologies of the middle 

 ear bones are, however, in some doubt (see K, pp. 80-82). 



3. Bones of the upper jaw. — The upper jaw, composed originally of the two 

 pterygoquadrate cartilages, is fused to the skull proper and forms its lateral 

 portions. It consists, in Necturus, in part of the persistent portions of the 

 pterygoquadrate cartilages, in part of the cartilage bones formed in these 

 cartilages, and in part of membrane bones ensheathing and replacing the 

 cartilage. 



a) Membrane bones of the upper jaw: The anterior tip of the jaw is formed 

 of the premaxillac, V-shaped bones, the angle of the V directed forward and 

 constituting the tip of the snout. One limb of the V is a slender process situated 

 dorsally on top of the anterior end of the frontal bone. The other limb of the 

 V is a tooth-bearing process forming the margin of the anterior end of the skull. 

 Posterior to the premaxilla is the tooth-bearing vomer already mentioned and 

 not regarded as a bone of the jaw. Posterior to the vomer is the palato pterygoid 

 bone, the anterior portion of which bears teeth. From the projecting angle to 

 which the lower jaw articulates to the posterior angle of the otic capsule extends 

 the slender squamosal bone. 



b) Cartilage bones of the upper jaw: The quadrate bone forms the fossa into 

 which the end of the lower jaw articulates and extends posteriorly from the fossa 

 for a short distance in contact with the inner side of the squamosal. Medial to 

 the quadrate bone is a considerable area of cartilage, the quadrate cartilage, 

 representing unossified portions of the pterygoquadrate cartilage. Besides the 

 quadrate bone, a portion of the palatopterygoid bone is likewise a cartilage bone 

 •ossified in the pterygoquadrate cartilage. 



Draw dorsal and ventral views of the skull, outlining the bones accurately. 



