The lumbar and sacral innervation of the Arctocephalus australis

Abstract

In order to describe the innervation originated from ventral lumbar and sacral branches, a study was made through dissection of two specimens of south american fur seals (Arctocephalus australis), originated from CRAM-FURG, where they arrived deceased. The nervous structures that constitute the lumbar and sacral plexes are originated from ventral branches of spinal nerves which come from medullary segments L1 to S3. Thus, one can observe that the nerves originated form L1 to L3 are monosegmentary, being respectively iliohypogastric, ilioinguinal and lateral femoral cutaneous nerves. From the reunion of L3 and L4 segments arise genitofemoral, obturator and femoral nerves. From the confluence of segments L4-5-S1 arises a nervous trunk - the sciatic plexus, which gives the following nerves: cranial and caudal gluteal, caudal femoral cutaneous and sciatic. Sciatic nerve splits into lateral and caudal sural cutaneous, tibial, common peroneal. Pudendal nerve (which divides into dorsal nerve of the penis or clitoris, deep and superficial perineal) and caudal rectal are formed from the S2-3 segments. With these data, one can conclude that the lumbar and sacral innervation have similar origin to other mammal species, however its organization and distribution reflect the adaptative changes to this animals' habits, specially its locomotion in water.