92 ANATOMY OF VEKTEBRATES. 



give passage to the gullet and the apex of the heart, expands 

 over the anterior part of the thoracic air-cells, and becomes, at its 

 lateral circumference, the point of attachment of muscular fibres 

 arising from the inner surface of the anterior ribs, and forming 

 apparently a continuation of the transversalis ahdominis. 



The appendico-costales^ arise from the posterior edge and ex- 

 tremity of the costal processes, and run down to be inserted 

 severally into the rib posterior to that to which the process 

 affording them origin is attached. These processes are supported 

 by strong triangular aponeuroses continued from their anterior 

 and upper margins, severally, to the rib anterior to them. 



The levator caudcB arises from the posterior and superior ex- 

 tremity of the ischium ; it is inserted into the spines of the caudal 

 vertebrae. In birds with a posteriorly expanded sacrum, that 

 bone affords the chief origin to this muscle, fig. 35, lo. 



The adductor caudcB superior is smaller than the preceding, 

 with which it runs parallel; it rises below from the posterior 

 extremity or tuber of the ischium, and is inserted into the pleura- 

 pophyses of the caudal vertebrae. 



The adductor caudce inferior arises from the tuber ischli and 

 the ligament connecting this with the posterior extremity of the 

 pubis. It is inserted into the diapophyses of the caudal vertebrae. 



The depressor caudcB arises, ib. 15, from the under part of the 

 middle line of pelvis ; it is Inserted into the inferior spines of the 

 caudal vertebrae. 



In birds of flight the ' rectrices,' or rudder-quills attached to 

 the coalesced and modified terminal vertebras call for moving 

 powers not developed in the Apteri/x. 



The quadratus coccijgis, fig. 35, ii, arises from the diapo- 

 physes of the coccygeal vertebra?, and is inserted into the shafts 

 of the tail-quills, which it separates and raises. On the lateral 

 aspect the puho-coccygeus, ib. 12, arises from the posterior margin 

 of the pubis, and inserted also into the shafts of the exterior rec- 

 trices ; it is by means of these muscles in conjunction with the 

 quadratus and levator caudal, that the Peacock raises the gorgeous 

 plumes overlying the true tail-feathers. 



The ilio-coccygeus, ib. 13, extends from the posterior margin of 

 the ilium to the last coccygeal vertebra, and to the small inferior 

 tail-feathers. 



On the ventral or inferior aspect of the tail, the muscles are in 

 general more feebly developed than on the opposite side, except 



' X1-. vol. iii. pi. 32, //» p. 287. 



