DISSECTION OF THE DOG 145 



region. Note the cutaneous branches of the intercostal nerves and the 

 vessels accompanying them. 

 The two dorsal serratus muscles demand first attention. 



M. serratus dorsalis cranialis.— The cranial dorsal serratus muscle 

 springs by a broad, thin aponeurosis from the ligamentum nuchae and the 

 spinous processes of the first six or seven thoracic vertebrae. The fibres run 

 in a ventral and caudal direction to be inserted by digitations into the ribs 

 from the second or third to the ninth or tenth. 



M. serratus dorsalis caudalts. — The caudal dorsal serratus muscle 

 arises from the dorso-lumbar fascia. Its fibres have the same direction as 

 those of the internal oblique muscle of the abdomen, with which it appears to 

 be continuous. The insertion of the muscle is into the last three ribs. 



Dissection. — Reflect the dorsal serratus muscles. 



M. longissimus dorsi, etc. — A powerful muscular mass lies in the groove 

 formed by the transverse and spinous processes of the lumbar vertebrae. On 

 a level with the last rib the mass divides into three muscles : ilio-costalis, 

 longissimus dorsi, and spinalis dorsi et cervicis. 



M. ilio-costalis. — The ilio-costal muscle leaves the common mass about 

 the last rib, and has attachments by independent tendons to the ribs about 

 their angles and the transverse processes of the last two or more cervical 

 vertebras. Each tendon passes over one or two ribs before finding insertion. 

 Slips from all the ribs except the first four or five join the muscle as it runs 

 along the wall of the chest. 



M. longissimus dorsi. — The fibres of this powerful muscle arise from the 

 ventral surface and crest of the ilium, and are attached to the transverse 

 processes of the lumbar, thoracic, and last cervical vertebrae, to the spinous 

 processes of the lumbar and thoracic vertebrae, and to the ribs. 



M. semispinals dorsi et cervicis cannot be completely examined at 

 the present time. 



Dissection. — Remove the longissimus dorsi muscle. In doing so, observe 

 the muscular branches of the dorsal rami of the intercostal and lumbar 

 arteries. 



M. multifidus. — A series of small muscles, larger in the lumbar than in 

 the thoracic region, arise from the sacrum and the articular and transverse 

 processes of the lumbar and thoracic vertebrae, and are inserted into the 

 spinous processes of these vertebrae. Each muscle passes over one spinous 

 process before its insertion. 



M. submultipidus. — In the thoracic region it is customary to find yet 

 shorter muscles underneath the multifidus. The bundles of the submultifidus 

 muscle pass from the transverse process of a vertebra to the spinous process 

 of the one immediately preceding it. 



