^o.4.\ SHUFELDT ON THE OSTEOLOGY OF SPEOTYTO. 93^ 



turned posterior extremities are about opposite tlie lower borders of the- 

 temporal fossae, its two limbs diverging from each other at an angle equal 

 to that made by the lower mandible. The cerato-hyals are rather large 

 in comparison with the other bones. They are joiued both anteriorly 

 and posteriorly by bony bridges, forming a fenestra between them, to 

 be filled in by a thin membrane. The amount of <livergence they make 

 from each other is less than that made by the hypo-branchial elements 

 of the thyro-hyals. Anteriorly, the bone connecting them supports a 

 cartilaginous glosso-hyal, while the posterior connection ])resents for 

 examination the usual smooth articulating surface that enters into tlie 

 arthrodial joint it makes with the basi-hyal. The basi-hyal and uro- 

 hyal are confluent, not a sign of the point of union remaining. The 

 latter bone is continued a short distance posteriorly by a tip of cartilage. 

 The anterior end of the basi-hyal is devoted to the articular surface for 

 the bone connecting the cerato-hyals, forming the joint mentioned above. 

 It is concave from above downwards, convex from side to side, the lower 

 lip being the longer. It will be plainly seen that this combination grants 

 to the tongue a movement in the vertical and horizontal planes. The 

 anterior articulating heads of the hypo-branchial elements of the thyro- 

 hyals are ojiposite each other, each being received into thedirainutive aceta- 

 bulum intended for it at the side of the united basi and uro-hyals, and 

 most probably at the junction of the two latter bones. These two ele- 

 ments are long bones having a cylindrical shaft, terminating at either 

 end in an articu'ating head. They are the longest bones in the hyoid arch, 

 and have a gentle curvature upwards throughout their extent The inner 

 heads form an arthrodial joint on either side with the outer heads of 

 the cerato-branchial elements of the thyro-hyals. These, the last bones 

 of the arch, are joiued in the manner already shown above. Their inner 

 ends are quite i)ointed, even as far as the bone goes, the extreme points 

 being finished off with cartilage. They curve upwards from about their 

 middle thirds, and, like the first elements of the thyro-hyals, they are 

 long bones, but with curved cylindrical shafts, the outer end, however, 

 being the only true articulating one. 



The lower onandihle — (Pis. I and II, Fig. 3.). — Tliat portion of the bone 

 which originally was separate as the dentary element, and as far hack as 

 to include the interangular vacuity, is firm and compact, while the re- 

 mainder has much the same character as the bones of the cranium, being 

 (jellular and light, having oidy a very thin outside layer of the liardcr 

 tissue. All of the primary segments are firmly knitted together, the only 

 sutural trace to mark the margins of any one of them being the posterior 

 border of the dentary elements as they bound the fenestra l)eforc ami 

 slope away beneath it. The articular extremities are some little distance 

 below the upper outline of the bone. Their superior surfaces are in- 

 dented so as to accurately receive the condyles of the tympanies on 

 either side, forming the joint that allows the o]ieniug and (Mosingof the 

 mandibles. Their under surfaces fire smooth and roaiidcd, liaving ii 



