458 ZOOLOGICAL EESULTS OF THE EUWENZOEI EXPEDITION. 



The brevis portion is of large size, extending the whole length of the humeral 

 shaft. With regard to its origin it may be noticed that, in addition to the usual 

 attachment to the os Immero-scapulare (text-fig. 16, o.h.s.), it has also a ligamentous 

 slip from the neck of the scapula. 



In Acrocephalus the longus division has similarly two points of origin, and fusion 

 between the two moieties does not take place till midway down the arm. The muscular 

 belly thus formed is continued downwards to be inserted in common with the tendon 

 of the brevis division. This tendon looks, indeed, as if it really belonged to the d. m. 

 brevis, and as if the longus division had grafted itself on to the brevis portion just before 

 this passes into tendon. 



Leg-Muscles. 



Of the leg-muscles of Brcuh/pterus only the gastrocnemius is of sufficient interest 

 to demand notice here. 



The external head is very thick, fleshy, and spindle-shaped ; the belly terminates in 

 a point rather below the middle of the tibial shaft, where it gives place to a long 

 tendon joined almost at once by the tendons of the middle and tibial heads. The 

 belly, at about its middle, and just below the biceps loop, sends off a thin sheet of 

 muscular fibres to the middle head. 



The tibial, like the external head, is very strongly developed, and ends in a point 

 running parallel with, and anchored to, the tendon proper to this head by a thin sheet 

 of tendinous tissue. The tendon, it will thus be seen, is rather peculiar, for, instead of 

 forming a continuation of the extremity of the fleshy portion of the muscle, it is given 

 off from the post-axial border of the belly — that is to say, the tendinous portion of 

 the muscle becomes concentrated rather high up, and not at the end of the muscle 

 as is usual. 



The middle head is short and thick, and sharply truncated distally, giving place 

 very suddenly to a tendinous sheet which runs parallel to, and is fused with, the tendon 

 of the tibial head just described. Lower down the leg, however, this tendinous sheet 

 develops a fairly well-marked and typical tendon along its middle, and this eventually 

 joins the tendons of the external and middle heads. But this head shows a decided 

 tendency to fuse with the tibial head, and this condition is actually reached in the 

 Whitethroat, where it passes into the tibial head near the middle of that division. 

 In Acrocephalus the middle head is extremely feeble, taking the form of a thin sheet of 

 muscle terminating abruptly as in Bradypterus, and attached, as it were, to a delicate 

 tendinous sheet stretched between the terminal halves of the fleshy bellies of the 

 external and internal heads. Not until this sheet has nearly approached the ankle- 

 joint is the characteristic tendon developed. 



Not the least interesting fact about the gastrocnemius of Bradijpterus is the fact 

 that the fused tendons of the external and tibial heads are ossified. This ossificatior. 



