126 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



12. The hyoid apparatus. — This is, as already explained, the remnant of th 

 hyoid and other gill arches. It is generally absent on prepared skeletons an 

 isolated specimens will be provided for its study. 



The hyoid of the cat consists of a bony bar placed in the root of the tongu 

 just in front of the larynx; this bar is called the body of the hyoid. From i 

 extend two pairs of processes or horns, an anterior pair and a posterior paii 

 The anterior horns consist of four separate pieces, of which the terminal piec 

 is attached to the tympanic bulla just ventral to the stylomastoid forame: 

 of the skull. The groove which it occupies can generally be seen on the side o 

 the bulla. The posterior horns consist each of a single piece which is united h 

 the larynx. The body and anterior horns belong to the hyoid arch; the posterio 

 horns to the third gill arch. The remaining gill arches are represented in th 

 larynx which will be studied later. 



The hyoid apparatus of the rabbit consists of a stout bone, the body of th 

 hyoid, situated at the base of the tongue in front of the larynx. It bears tw< 

 pairs of processes or Itonis. The anterior horn is a short piece connected by ; 

 muscle with the jugular process of the skull. The posterior horn is a longe 

 piece connected by ligament with the larynx and by muscle with the jugula 

 process. The body and anterior horn are remnants of the hyoid arch, the posterio: 

 horn of the third gill arch. 



H. GENERAL SUMMARY OF THE SKULL AND VISCERAL SKELETON 



i. The skull begins as a cartilaginous case, the chondrocranium, whose method o 

 formation has already been described. This case includes the olfactory and otic 

 capsules. 



2. The gill arches become closely associated with the chondrocranium. There an 

 usually seven of them, the first forming the upper and lower jaws, the second the hyoid arch 

 The arches are reduced in number and altered in function in land vertebrates. 



3. Bones derived from the chondrocranium and gill arches are the cartilage bones o: 

 the skull. 



4. In addition to these there are membrane bones added. They come from the dermi: 

 of the skin and were originally dermal scales. 



5. The cartilage bones of the skull and sense capsules are the occipitals, sphenoids 

 ethmoids, otics, and turbinals. There are four occipitals (supraoccipital, two exoccipitals 

 basioccipital) ; a posterior group of three sphenoids (basisphenoid, two alisphenoids) ; ar 

 anterior group of three sphenoids (presphenoid, two orbitosphenoids) ; and a group of thref 

 ethmoids (mesethmoid, two ectethmoids). The otic bones ossified in the ear capsule an 

 generally three in number but may be as many as five; in mammals they are fused to forrr 

 a periotic or petromastoid bone. The nasal capsules may furnish additional cartilage bones 

 The occipitals and sphenoids form the posterior end and floor of the brain cavity, while th( 

 ethmoids inclose the nasal cavities. 



6. The first gill arch generally gives rise to two cartilage bones, a quadrate derived froir 

 the posterior end of the upper jaw cartilages or pterygoquadrate cartilages; and an articula: 

 derived from the posterior end of the lower jaw cartilages or Meckel's cartilages. In somi 

 forms the pterygoquadrate cartilages may give rise to palatines and pterygoids in addition 



