110 
PEOFESSOE WOOD OX THE NECK- AND SHOULDEE-MUSCLES . 1 
There is another muscle, almost universal in the Mammalia, which may be considered 
perhaps to be a part of the same apparatus as the rectus muscle ; but which is confined, 
even in the most highly developed instances, to the upper part of the thorax. It is 
described by Cuvier under the name of the sterno-costcdis. In many respects this muscle 
agrees better in its homological bearings with the abnormal human sujoracostalis than 
the rectus thoracicus does. Besides being confined to the upper part of the thorax, the 
upper attachment of the muscle is always in close relation to the insertion of the anterior 
scalenus , as in the human abnormality. This is well seen in the Dog (Plate XI. fig. 2 7, n), 
where it is connected below, not to the sternum as in many Mammalia, but to the 
second and third costal cartilages and intercostal aponeurosis, and does not reach any- 
where near the insertion of the rectus abdominis. The same arrangement is found also 
in the Badger. In the Rabbit the muscle is short, but broad, and reaches from the first 
rib and to the cartilage of the second rib, extending inwards as far as to the sternum 
(see Plate X. fig. 16, B, n) ; while the rectus thoracicus reaches only up to the second 
rib, the most common upward limit in the Mammalia generally. It is not mentioned 
by Krause in his description of this animal. In cases in which the rectus extends to 
the first rib, the sterno-costal muscle usually overlaps it (see figs. 18 & 26, n), assuming 
an oblique position on the thorax. It is always attached to the first rib close to the 
inner side of the origin of the scalenus anticus , and thence passes obliquely downwards 
and inwards between the upper end of the rectus thoracicus and the pectoral system 
of fibres, the pectoralis minor and sterno-clavicular both lying superficial to it. The 
rectus thoracicus itself is attached to the first rib and its cartilage, always closer to the 
sternum, and much internal to the upper attachment of the sterno-costal , and never has 
so intimate a relation with the scaleni as the last-named muscle. In this respect espe- 
cially the human supracostal muscle resembles the sterno-costal of animals much more 
than the rectus thoracicus. In the Mammalia generally the sterno-costal is a more or 
less triangular muscle, but sometimes tapers off below before it joins at the sternum with 
the deeper pectoral fibres, of which it always forms the deepest layer. It is covered by 
a fascia derived from that of the rectus thoracicus and intercostcils. In the Quadru- 
mana the sterno-costal is usually large. In the Bonnet-Monkey it reaches and crosses 
the upper part of the rectus thoracicus as low down as the second and third rib (see Plate 
X. fig. 12, n). In the Magot it is enormous, as figured by Cuvier and Laurillard, 
arising by digitations from the three upper ribs, and passing downwards and inwards to 
the three upper pieces of the sternum. In the Pajoio Mormon it is attached to the first 
rib above, and below to the second and third costal cartilages. In the Marmoset and 
Lemur macaco it arises from the first rib close to the scalenus , and crosses, as in the 
Carnivora generally, the upper fibres of the rectus thoracicus. It is found in the Hedge- 
hog and Tenrec ; and according to Cuvier, in the Black Bear, Coati, Panther, Lion, 
Hyiena (very large), Badger, Genette, Seal*, and Polecat. In the Panther a slip of 
* In Ills paper on the Myology of the Cape Anteater and Seal, Professor Humphry describes, in the latter 
animal, under the name of the subclavius, a muscle “ thin from the margin of the sternum opposite the second. 
