THE SPECIAL ANATOMY OF THE FROG 53 



which the medulla oblongata passes to become continuous with the spinal cord. 

 Ventrally they bear two rounded prominences, the occipital condyles, by which 

 the skull articulates with the atlas. 



(5) Pro-otic bones, the cartilage bones extending laterally from the posterior 

 end of the frontoparietals. They are ossified in the otic capsule and hence inclose 

 the ear. 



The bones of the upper jaw or maxillary arch are : 



(1) Premaxilla, a pair of small membrane bones in front of the external 

 nares. 



(2) Maxilla, the long slender membrane bone forming the greater part of the 

 sides of the jaw. Premaxillae and maxillae bear teeth. 



(3) Quadratojugal, the short slender membrane bone behind the maxilla, not 

 bearing teeth. 



(4) Squamosal, the curious T-shaped membrane bone extending from the 

 posterior end of the quadratojugal to the pro-otic. 



(5) Pterygoid, a three-rayed cartilage bone under the squamosal but visible 

 from the dorsal side. 



(6) The quadrate cartilage lies between the squamosal and the pterygoid and 

 is the place of attachment of the lower jaw to the skull. 



b) Ventral aspect of the skull. The ventral bones of the skull are: 



(1) Vomer, a pair of membrane bones behind the premaxillae, forming the 

 floor of the olfactory capsules and bearing teeth. 



(2) Palatine, two slender cartilage bones extending laterally from just 

 behind the vomerine teeth to the maxillae. 



(3) Parasphenoid, a single long dagger-shaped membrane bone on the ventral 

 surface of the skull, its lateral posterior processes underlying the auditory 

 capsules. The point of the dagger underlies the ventral side of the sphenethmoid 

 ring. 



c) The bones of the lower jaw or mandibular arch. These are: 



(1) Mentomeckelian bones, two small cartilage bones at the tip of the lower 

 jaw. They are ossified in the original cartilage bars (MeckePs cartilage) which 

 were the lower jaw of the tadpole. 



(2) Dentary, a short membrane bone behind the preceding on the outer surface 

 of the jaw. 



(3) Angulosplenial, the long slender membrane bone forming the greater 

 part of the jaw. Its anterior end is under the dentary. Its outer surface behind 

 the dentary is grooved. In this groove is located in life MeckePs cartilage, which 

 articulates with the quadrate cartilages of the skull. 



d) Hyoid apparatus. This portion of the skeleton is usually lacking in dried 

 material. Most of its parts have already been seen during the dissection of the 

 frog and should be examined again and further exposed in your preserved speci- 

 men (Holmes, p. 324). 



