MUSCLES OF THE SHOULDER AND ARM. 33 
9. The Deltoid Muscle. In the dog it is divided 
into two separate muscles, not including the portion 
of the levator humeri which corresponds to the clavo- 
deltoid. 
a. The acromio-deltoid, the smaller division, takes 
its origin from the acromion process, and is inserted 
into a ridge along the outer surface of the proximal 
third of the humerus. 
b. The spino-deltoid arises by a strong fascia from 
the posterior border of the spine of the scapula along 
most of its extent, and is inserted into the humerus to- 
gether with tne acromio-deltoid. 
Cut through the bellies of the deltord muscles, and 
reflect the cut ends. 
10. The Infra-spinatus Muscle fills up the infra- 
spinous fossa from which it arises. Its fibres end 
_ ina strong tendon which is inserted into the great 
tuberosity of the humerus just below the insertion of 
the supra-spinatus. 
11. The Teres Minor is seen just posterior to the 
infra-spinatus near its insertion. When dissected out 
it will be found to arise along the posterior margin of 
the scapula by a tendinous expansion lying beneath 
the infra-spinatus. It is inserted into the humerus 
below the great tuberosity. 
12, The Latissimus Dorsi is a very large muscle 
arising by a fascia from the spinous processes of the 
lumbar and posteroir thoracic vertebra. From this 
origin the fibres form a wide sheet of muscle lying on 
the dorso-lateral wall of the thorax, and converge 
anteriorly toward the humerus. It ends ina tendinous 
expansion which fuses with the sheath of the triceps 
medius and teres major, through which its action on 
the humerus takes place. Just before its insertion the 
