164 



ANATOMY OF VERTEBRATES. 



second is in close proximity with, and to tlie right side of the pre- 

 ceding, leading to the dnodenum, ib. o; below these apertnres 

 the cavity extends to form a cu^de-sac, c. At the middle of the 



anterior and posterior parts 

 of the cul-de-sac there is a 

 tendon, figs. 78, 79, e, from 

 which the muscular fibres 

 radiate. 



The differences in the 

 structure of the gizzard 

 resolve themselves into the 

 greater or less extent of 

 the tendons, and the greater 

 or less thickness of the 

 muscular coat, and of the 

 lining membrane. 



In the Rajjtores the giz- 

 zard, fig. 78, d, assumes 

 the form of a mere mem- 

 l^ranous canity, in accord- 

 ance mth the animal and 

 easily digestible nature of 

 their food. The muscular 

 coat is thin ; the fibres prin- 

 cipally radiate from small 

 tendons, ib. e, and there are some longitudinal fibres beneath the 

 radiating or external layer. 



In the Rasores and lamelKrostral Natatores it exhibits the 

 structure to which the term gizzard can be more appropriately 

 applied, figs. 83, 84, The muscular fibres are distinguished by 

 their unparalleled density of texture and deep colour, and are 

 arranged in four masses ; two are of a hemispherical form, and 

 their closely-packed fibres run transversely to be connected to 

 very strong anterior and posterior tendons, fig. 84, e ; they con- 

 stitute the sides of the gizzard, and are termed the digastric 

 muscles or ' musculi laterales,' fig. 83, di between these, at the 

 end of the gizzard, are the two smaller and thinner muscles called 

 ' musculi intermedii,' fig. 84, /. There are likewise irregular 

 bands placed about the circumference of the gizzard. 



Fig. 83 shows the relative thickness of the musculi laterales in 

 the gizzard of a S^Yan, and fig. 84 that of the musculi intermedii 

 and tendon. 



The internal coat of the gizzard, fijr. 84, <?, /i,is extremely liard 



Gizzard of a Swan. 



