24G Mli. G. P. MUDGE ON THE MYOLOGY 



TuE Hypoglossus Muscle. 



(f<) l/z/pof/lossus obliqnus. — The variations exhibited by this muscle may be considered 

 under three heads : 1st, the amount of its extension backwards upon the hypobranchial ; 

 2nd, the degree of development of its ten<lon or tendinous fascia ; 3rd, its divided or 

 undivided condition. The advance of an individual muscle in respect of any one of 

 these characters is not always accompanied with a corresponding advance of the other 

 two ; but if the muscles are arranged in sets, each set representing a stage in the 

 progression of one of these three characters, it will be found that the majority in each 

 set are advanced in respect of the other two characters. 



The muscle arises in part from the hypobranchial and in part from the ventral and 

 dorsal surfaces of the body of the basihyal, and is inserted into the inner surface and 

 posterior margin of the 2)Osterior lateral process of the entoglossum. In some Parrots 

 (Pis. XXVllI. & XXIX. figs. 29 & 48) {cf. pp. 266-269) the muscle (h^.o.) is divided 

 into two in a longitudinal direction, in such a way that an outer portion related to the 

 hypobranchial is separated from an inner one related to the basihyal, both retaining 

 the origin insertion. But in Lorius the plane of division does not thus divide the 

 muscle, for the outer portion is related both to the hypobranchial and basihyal 

 (PL XXIX. fig. 37). 



Stage 1. 

 The most primitive condition of the muscle is that in Avhich its origin is almost 

 wholly confined to the basihyal, and posteriorly does not extend farther than to the 

 anterior head of the hypobranchial ; it is further generally characterized by the absence 

 of a tendon or tendinous fascia and by the fact that it is not divided into two portions. 

 {Cf. the table of characters oi Hypoglossus obliqims, pp. 2G6-269.) 



Stage 2. 

 In this stage the muscle has extended backwards as far as the anterior third or 

 half of the hypobranchial. The fascia is usually tendinous or a weak tendon is 

 developed ; but in some few instances (Nestor) a strong tendon is present. The 

 muscle is divided in about 60 per cent, of the Parrots. 



Stage 3. 



The muscle extends to the anterior two-thirds of the hypobranchial, and in most 

 instances the tendon is fairly strongly developed, and in a few strongly; in one 

 [Deroptyus) it is absent, and neither is the fascia tendinous. The muscle is divided 

 in all except three. 



Stage 4. 



This is the final stage, and it is marked by the extension of the muscle to tlie 

 posterior extremity of the hypobranchial; in all instances the tendon is strongly 

 developed, and in a few instances very strongly so. The muscle is divided in all, with 

 but two exceptions. 



