136 
PROFESSOR A. MACALISTER ON THE 
and Laurillard figure this muscle as the petit pectoral ; Humphry regards it as a part 
of the great pectoral, and corrects Cuvier’s error of assigning to it a costal origin. The 
fact of this muscle and the pars sternalis receiving their nervous supply from the ante- 
rior thoracic nerve, a branch of the external cord of the brachial plexus, settles the 
question of its morphological nature. 
Pectoralis minor is absent in every species. 
Pectoralis quartus in all is a distinct, well-developed muscle, largest proportionally 
in Noctulina , smallest in the Pipistrelle, and very small in Scotophilus hesperus. In 
general it arises from the superficial fascia of the abdomen opposite the level of the 
low 7 er margin of the thorax, at the anterior termination of the upper false ribs ; in no 
case did its origin stretch as a separate structure to the pubis, and it invariably was di- 
stinctly superficial to the rectus abdominis ; and even when I detached artificially a slip 
of the fascia to make a factitious origin, it lay over and not alongside, or in any sense 
in common with the rectus, as Professor Humphry describes. In Ceplialotes its origin is 
from the middle line of the abdomen at its middle point, and its fleshy fibres overlie 
those of the rectus, crossing them at a small angle ; in this species it passes underneath 
the pars sternalis of the great pectoral to be inserted into the uppermost point of the 
pectoral crest of the humerus, immediately inferior to the insertion of the pars clavicu- 
laris. In all the species except Plecotus it was perfectly detached from the great pec- 
toral, and in that species it was merely connected with it at its insertion. In every 
other instance the muscle ended in a long tendon, by which it is inserted into the 
summit of the pectoral crest. In Pteropus edulis its origin corresponds to the linea 
alba, an inch below the ensifonn cartilage, and extending down for one fourth of this line. 
Its origin is always superficial, and below the great pectoral; but owing to the greater 
verticality of its fibres it soon sinks under cover of that muscle. In Pteropus and its 
allies the insertion is, as described by Professor Humphry, into the point below the pars 
clavicularis. In Vampyrops vittatus and Artibeus jamciicensis it is also below, but not 
quite in contact with the other muscle. In Vespertilio and Scotophilus it is behind the 
pars clavicularis. It is thin and inserted higher up in Megaderma . In Eleutherura 
it arises from the middle line of the upper third of the abdomen, also superficial to and 
separate from the rectus, and it extends even over the ensifonn cartilage. This muscle 
is regarded by Cuvier and Lx\urillard as the portion ventrale of the great pectoral, and 
by Professor Humphry is considered as probably the representative of the pectoralis minor 
( loc . cit. p. 301). It is, however, a muscle of a different nature, one whose synonyms 
are numerous, and which has been recognized as a distinct muscle by Professor Humphry 
in the Orycterope and Seal, under the name of brachio-lateralis* . In Man it often 
* The names given to this muscle in different animals are legion. It has been called humero-abdominalis 
(Klein), abdomino-humeralis (Duges), costo-humeralis (Huxley), chondro-epitrochlear (Duvernoy), brachio- 
abdominalis (Zeneer), brachio-lateralis (Humphry"), portio-abdominalis pectoralis majoris (Ecker). Pectoralis 
quartus, the name given to it above, was settled on by Professor Hauohton and myself as the name by which 
we should call it. 
