THE SHOULDER GIRDLE AND PECTORAL FIN OF FISHES. 
561 
that part v certainly, and parts i and ii probably, should be regarded as derivatives 
of the latero-ventral portion. Embryological evidence would be of interest here, as 
in other problems connected with Lophius. 
(c) Retractor mesio-ventralis pectoralis . — The latero-ventral portion has been 
seen to decrease in width as it approaches the anterior end, and in some cases 
completely to disappear. With this decrease of the latero-ventral, the mesio-ventral 
portion increases in proportion, so that it becomes attached to almost the whole 
length of the cleithrum. It is divided into two distinct portions, the superior (i) 
and the inferior ’(iii), while the medius (ii) portion, axillary, so constant in Elasmo- 
branchs, is vestigial. 
(i) R.m.v.p. superior. Subcoracoideus, Owen; Lateralis 4 (pars), M‘Murrich. 
A broad thin sheet of muscle, usually traversed by myocommata, inserted along 
the posterior border of the cleithrum and, in part, on the coracoid. The insertion is 
entirely dorsal to that of the fin muscles, and extends nearly to the dorsal end of the 
cleithrum. In this muscle the post-clavicle, when present, is embedded. 
(ii) R.m.v.p. medius. 
There is a triangle of connective tissue immediately behind the pectoral fin, and 
this is traversed by a few muscle fibres, which are inserted on the adductor muscle 
of the fin. These fibres are the only trace of a “ medius” in most Teleostei, but in 
Trigla (fig. 21) the muscle shows considerable development. 
(iii) R.m.v.p. inferior. Protractor ischii, Owen; Lateralis 5, M‘Murrich ; 
Pelvico-clavicularis, Hamburger. 
This muscle is attached to the cleithrum from just below the fin muscles to the 
ventral symphysis, where it meets its fellow of the opposite side, with which it 
is continuous. In those forms whose pelvic fins are thoracic or jugular in position 
this muscle becomes considerably specialised, and ceases to show the myocommata 
which are characteristic in lower types ; it may then be described as a pelvico- 
cleithrale (fig. 21). 
(3) The Anterior Muscles. 
A. Connections with the Skull. 
(a) Protractor pectoralis, Lambeau, Cuvier ; Protractor scapulae, Owen ; 
Occipito-clavicularis, Vogt and Yung, Hamburger ; Trapezius, 
Humphry, M‘Murrich. 
This muscle is constantly present in Teleosteans. It takes the form of a fan- 
shaped mass which, arising from the otic region of the skull, becomes inserted partly 
into the forward border of the supraclavicle and partly into the cleithrum. The 
muscle is superficial in position, and forms the posterior border of the upper portion 
of the gill cavity. 
