is from the anterior
edge of the sternal portion of the first four thoracic ribs. This
triangular muscle narrows and inserts on the posterior edge of the apex
of the costal process. The portion arising from the first rib may share
slips with _M. sternocoracoideus_.

~_M. costi-sternalis anterior_~, Figs. 1, 2, and 3. This muscle is
variously developed, and originates from a small area on the ventral end
of the vertebral portion of the last cervical rib. The insertion is on
the apex of the costal process, immediately anterior to the insertion of
_M. costi-sternalis_.

~_Mm. intercostales externus_~, Fig. 1. These muscles extend
posteroventrally between the vertebral portions of successive thoracic
ribs, and between the last cervical and first thoracic ribs. In the more
posterior intercostal spaces these muscles are poorly developed, but
they become progressively better developed anteriorly, and are fully
represented in the most anterior intercostal spaces.

~_Mm. intercostales internus_~, Fig. 3. These muscles resemble the
external intercostal muscles, but extend anteroventrally, with the
muscles being most fully developed posteriorly, and progressively less
so anteriorly.

~_Costopulmonary muscles_~, Fig. 3. This diagonal series of muscle slips
from the thoracic ribs attaches to the aponeurosis covering the lungs.

Angiology

Figs. 3 and 4 show all arteries discussed for this family. The numbers
following the names or descriptions of arteries in the text refer to
numbered arteries in one or both of these figures.

The right and left innominate or brachiocephalic arteries arise from the
aortic trunk and give rise to the common carotid arteries (14). The
major vessel continuing across the thoracic cavity is the subclavian
artery. Classically the subclavian is considered as continuing into the
anterior appendage as the axillary artery. However, in the species
studied, the axillary artery can best be described as a branch from the
subclavian; the pectoral stem forms a more direct continuation of the
subclavian. In traversing the thoracic cavity, the subclavian gives rise
to the thoracic, coracoid, and axillary arteries, and leaves the
thoracic cavity as the pectoral trunk, dorsal to the area where _Mm.
coracobrachialis posterior_ and _sternocoracoideus_ span the angle
formed by the coracoid and costal process.

The pectoral trunk bifurcates into two main pectoral arteries (9), which
penetrate _M. pectoralis tho