in.] THE CRANIAL SKELETON. 123 



spines of the anterior (most pre-axial) vertebrae by a very 

 strong ligament which prevents the mouth from being widely 

 opened. This is the case in the Eft Desmognathus. 



32. That very subordinate bone of the human skeleton, the 

 OS HYOIDES, or tongue-bone, is but a feeble rudiment of 

 skeletal structures of great size and functional importance 

 in the lower Vertebrates. Even less than the temporal bone 

 is it capable of revealing its true nature when studied in 

 man alone. 



Small, however, and subordinate as is the os hyoides in 

 him, it may yet be more rudimentary still. Thus osseous 

 parts may be entirely absent, and only represented by two 

 delicate cartilages, as is the case in Serpents. 



Throughout man's class we find a substantially similar con- 

 dition to that which exists in him. That is, we find a body 

 and a pair of cornua, and almost always a pair of cornicula, 

 but the proportions of these parts one to another, and their 

 degree of segmentation, vary. 



r iG. in. Hyoid of a Flying Fox (Pteropus), showing the much greater length 



of the cornicula than of the cornua. 



I, body of the hyoid ; sh, corniculum divided into three segments -stylo-hyal, 

 epi-hyal, and cerato-hyal ; th, the cornua of the os hyoides, or thyro-hyal. 

 (From Flowers "Osteology.") 



Thus the cornicula may abort altogether, as in some Apes. 

 >r they may be large, and represented by three distinct ossi- 

 ications, named respectively (from above downwards) stylo- 

 hyal, epi-hyal, and cerato-hyal, as is the case in the Flying Fox 

 and in the Dog. These cornicula are normally connected with 

 that process of the under surface of the petrous portion of the 

 temporal bone which has been named the tympano-hyal. 

 The lowermost of these three pieces may send out a process 

 and meet its fellow of the opposite side in front of the body 

 of the bone, as is the case in the Hyrax. 



The cornua are more constant in the degree of their 

 development in Mammals. They may be of large size, as 

 in the Thylacine, but never present the segmented con- 

 dition we so often find existing in the cornicula. They are 

 perhaps at about their maximum of relative size among 

 Mammals, in the Horse. 



