EPISKELETAL AND HYPOSKELETAL MUSCLES. 46 



In the lowest Verteirata — as, for example, in ordinary 

 fishes — the chief muscular system of the trunk consists of the 

 episkeletal muscles, which form thick lateral masses of longitu- 

 dinal fibres, divided by transverse intermuscular septa into 

 segments (or Myotonies) corresponding with the vertebrae. 

 The lateral muscles meet in the middle line below, and divide, 

 in front, into a dorso-lateral mass connected with the skull, 

 and a ventro-lateral attached, in part, to the pectoral arch, and, 

 in part, continued forward to the skull, to the hyoidean appa- 

 ratus, and to the mandible. Posteriorly, the lateral muscles 

 are continued to the extremity of the tail. The hyposkeletal 

 muscular system appears to be undeveloped. 



In the higher Vertebrata, both the episkeletal and hypo- 

 skeletal muscular systems are represented by considerable 

 numbers of more or less distinct muscles. The dorso-lateral 

 division of the lateral muscle of the fish is represented bj' the 

 superior caudal muscles, and by the erector spinai ; which, as 

 it splits up, anteriorly, and becomes attached to the vertebrse, 

 and to the ribs, and to the skull, acquires the names of spi- 

 nalis, semispinalis, longissimus dorsi, sacrohimbalis, it iter- 

 transversalis, levatores costarum, complexus, spleiiius, recti 

 postici, and recti laterules. 



The ventro-lateral division of the fish's lateral muscle is 

 represented, in the middle line of the trunk and head, by a 

 series of longitudinal muscles ; and, at the sides, by obliquely- 

 directed muscles. The former are the recti abdominis, extend- 

 ing from the pelvis to the sternum — the sterno-hyoidei, be- 

 tween the sternum and the hyoidean apparatus- — the genio- 

 hyoidei, which pass from the hyoid to the symphysis of the 

 mandible. The latter are the obliqui externi of the abdomen 

 — the external intercostales of the thorax — the svbclavius 

 stretching from the first rib to the clavicle ; the scaleni from 

 the anterior dorsal ribs to the cervical ribs and transverse 

 processes, and the sterno- and cleido-mastoidei from the ster- 

 num and clavicle to the skull. 



The fibres of all these oblique muscles take a direction, 

 from parts which are dorsal and anterior, to others which are 

 ventral and posterior. 



The trunk muscles of the lower AmpJiibia exhibit arrange- 

 ments which are transitional between those observed in Fishes 

 and that which has been described in Man, and which substan- 

 tially obtains in all abranchiate yertebrata. 



The muscles of the jaws and of the hyoidean apparatus 

 appear to be, in part, episkeletal, and, in part, liyposkeletal, 



