688 MR. G. E. DOBSON ON THE [JuDe 1 , 



hyal and ceratohyal bones being connected with the base of the 

 tong;ne by the membranous walls of the pharynx alone. 



The hyoid bone (figs. 1, 2, 3) is remarka'bly formed : the basi- 

 hyal is ankylosed behind to a pair of long spatulate thyrohyals ; in 

 front it articulates on either side by a synovial joint, permitting 

 very free rotatory motion, with a cartilaginous ceratohyal, which 

 also articulates by its upper extremity with a large, very pecuharly 

 shaped cartilaginous epihyal, which is circular in outUne, having 

 its inner side flat or slightly convex, its outer deeply concave from 

 below backwards and upwards, and near its articular extremity a 

 prominent external projection, across which the tendons of the mylo- 

 hyoid and hyo-glossus muscles, above described, ghde ; the cerato- 

 hyal muscle extends from its posterior margin to the thyrohyal 

 bone ; and the stylo-hyoid muscle is inserted into its upper side. Its 

 outer surface, as above described, is deeply concave in the adult 

 male, and is lined by part of the neck of a sac, which extends out- 

 wards and backwards from the pharynx, under cover of the integu- 

 ment and the sterno-mastoid muscle, across the clavicle to the antero- 

 inferior part of the thorax. Another sac, anterior to this, on each 

 side of the neck, also extends outwards from the pharynx, and will 

 be described further on {vide infra, fig. 4). 



The walls of the evidently highly extensible pharynx are at- 

 tached anteriorly to the base of the skull and to the hack of 

 the fauces and tongue (which is free between the hyo-glossi and 

 stylo-glossi muscles ; for there is no trace of genio-byoid or genio- 

 hyo-glossi muscles, and the body of the organ appears to be chiefly 

 made up of a few muscular fibres with much interposed fat), 

 extending forwards for some distance between its inferior surface 

 and the mylo-hyoid expansion — posteriorly, to the anterior margins 

 of the basi-, cerato-, and epihyal bones, and laterally, by an 

 oblique ligamentous band, to the sterno-mastoid muscles. Imme- 

 diatelj^ behind the mouth, in the adult male, are two large oval 

 apertures (04 inch in antero-posterior diameter) in the sides of the 

 pharynx, leading into a pair of large sacs, which extend outwards 

 under cover of the integument beneath and behind the ears. The 

 apertures open opposite each other ; so that, if the sacs be cut open 

 from without, the pharynx appears to be transfixed. These, which 

 may be called the anterior pharyngeal sacs, are separated on each 

 side of the neck from the posterior pharyngeal sacs (above described) 

 by the sterno-mastoid muscle, and by a ligamentous septum passing 

 inwards from it to the side of the pharynx, and outwards to the 

 integument. Both pairs of sacs are absent in the female ; their pre- 

 sence therefore indicates a secondary sexual character, of which the 

 nearest analogue in Mammals appears to be the laryngeal sac of the 

 Orang*. 



^ It is an interesting fact that the nearest known analogues of these pharyn- 

 geal sacs are to be found not among Mammals but in Birds, as in certain species 

 of Otis and Tetrao. This might lead us to think that this pecuh'ar secondary 

 sexual character was in some way related to the volant powers of the animals. It 

 must, however, be recollected that these birds are noted for their terrestrial habits. 



