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Lab Objectives:

• Reflect skin from the caudal half of the right side and look for superficial inguinal lymph nodes
   and cutaneous vessels:
      - caudal superficial epigastric a. (from the external pudendal a.)
      - look for superficial arterial branches from the four quadrant abdominal blood supply

• Examine ventral branches of lumbar spinal nerves and their lateral cutaneous nn.,
   especially the lateral cutaneous femoral n. (last lateral cutaneous nerve).

• Identify the inguinal canal and its contents:
      - external pudendal vesels and genitofemoral n.
      - vaginal process (female) or spermatic cord (male)

• In the male, examine: testis, epididymis, spermatic fascia (external & internal),
   cremaster m. (dog), and components of the spermatic cord:
      - vaginal process (parietal, visceral, & connecting tunics)
      - ductus deferens and testicular vessels

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Anatomical Terms:

Ventral & Lateral Abdominal Wall
        external pudendal a.
                caudal superficial epigastric artery
        superficial inguinal lymph nodes
        cranial abdominal a.
        deep circumflex iliac a. & v.
        lumbar spinal nn. (ventral branches)
                cranial iliohypogastric n. (L1 ventral branch)
                caudal iliohypogastric n. (L2 ventral branch)
                ilioinguinal n. (L3 ventral branch)
                lateral cutaneous femoral n. (from L4 ventral branch)

Inguinal Structures
        inguinal canal
                external pudendal a. & v.
                genitofemoral nerve

                         MALE
        spermatic fascia (external & internal)
        cremaster muscle (dog; usually absent in cats, they have a levator scroti m.)
        spermatic cord
                vaginal process
                        parietal & visceral vaginal tunics
                        mesorchium
                        mesoductus deferens
                ductus deferens
                        deferent artery/vein
                testicular artery/vein
                        pampiniform (venous) plexus
        testis
        epididymis (head, body, tail)
                ligament of the tail of the epididymis
                proper ligament of the testis
        scrotum

                         FEMALE
        vaginal process
        round ligament of the uterus

        Note:
             vaginal [Latin] = sheath

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Instructor Commentary:

The scrotum is always located between the anal canal and the penis (in the prepuce). In the cat, the penis is directed caudally and the scrotum is positioned just below the anal canal.

The dog (and most male mammals) have a cremaster muscle to bring the testis close to the body wall. Most cats lack a cremaster m. (it would have to curve to reach the testis); instead, cats have a levator scroti m. that originates from the external anal sphicter, attaches to the scrotal septum, and pulls the entire scrotum closer to the body.

Spermatic fascia surrounds the spermatic cord and lines the scrotum. It is derived from transversalis and subcutaneous fascia of the abdomen and it envelops the parietal tunic of the vaginal process. Spermatic fascia is sometimes divided into internal and external components. Internal spermatic fascia forms a strong membrane to the inside of which parietal vaginal tunic is attached. External spermatic fascia is a loose areolar tissue that surrounds internal spermaltic fascia.

The testicular artery snakes back and forth and testicular veins undergo profuse branching (pampiniform venous plexus). This creates an extensive area of arteriovenous contact for heat conservation. Arterial heat is gradually transferred to returning venous blood with two big benefits: The testes remain cool (the reason they are subcutaneous in the first place) and body heat is conserved (the majority of food calories are required to maintain body heat).

In cervical and thoracic regions, ventral branches of spinal nerves are identified by number, e.g., C-3; T-6; etc. In the lumbar region you can identify the first three ventral branches by number or by name:
                L1 = cranial iliohypogastric n.
                L2 = caudal iliohypogastric n.
                L3 = ilioinguinal n.

Beginning with L-4, spinal nerve ventral branches contribute to the lumbosacral plexus. However, the L-4 ventral branch does give rise to the last of the series of lateral cutaneous nerves. The cutaneous nerve is larger than other and it is named "lateral cutaneous femoral nerve".

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Dissection Images:

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