472 ANATOMY IN A. NUTSHELL. 



The allantois is a fetal appendage of most vertebrates, developing as a sac 

 or diverticulum from the posterior portion of the intestinal cavity. It is one 

 uf the organs of the embryo of all amniotic vertebrates, or those which develop 

 an amnion, but is wanting or is most rudimentary in amphibians and fishes, 

 In birds and reptiles it is large and perforins a respiratory function, and in 

 mammals contributes to form the umbilical cord and placenta. Its exterior 

 primitively consists of mesoblast, its cavity receiving the secretion of the pri- 

 mordial kidneys (Wolffian bodies). So much of the sac as remains pervious 

 within the body of the embryo becomes the urinary bladder, or in some degree 

 a urinary passage. 



The umbilical arteries and veins course along the elongated stalk of the 

 sac, which becomes the umbilical cord, and that part of these allantoic vessels 

 within the body which does not remain pervious become the urachus and round 

 Ligament of the liver. 



The expanded extremity of the allantois, in most mammals, unites with 

 the chorion to form the placenta. In those vertebrates, as mammals, in which 

 the umbilical vesicle has but a short period of activity, the allantois chiefly 

 sustains the functions whereby the fetus is nourished by the blood of the mother 

 and has its own blood arterialized. In parturition, so much of the allantois 

 as is outside of the body of the fetus is cast off, the separation taking place at 

 the navel. 



The uvula vesica? is a slight projection of mucous membrane from the 

 bladder into the cystic orifice of the urethra. 



The arteries of the bladder are the superior, middle and inferior vesical and 

 in the female the uterine and vaginal also; its veins are radicles of the internal 

 iliac. The Lymphatics accompany the veins and terminate in the internal iliac 

 gland. The nerves are derived partly from the sympathetic system through 

 the hypogastric plexuses, partly from the cerebro-spinal system through the 

 third and fourth sacral nerves. The former supply the mucosa, the latter of 

 the muscularis. 



The bladder is held in place by ligaments which are divided into true and 

 false. The true ligaments are five in number; the two anterior, two lateral, 

 and the urachus (superior). Tin: false ligaments, also five in number, are 

 formed by folds of the peritoneum. The false are named the two posterior, 

 two Lateral and superior. 



LESSON CLII, 



The word urethra (Plates CCLXXII-CCLXXIX) is derived from the Greek 

 which means to urinate. The male and female urethrae differ. It is a modifica- 

 tion of a pari of a uro-genital sinus into a tube ora groove for the discharge of 

 the secretion of the genital <>r urinary organs or both; in most mammals, in- 

 cluding man, a complete tube from the bladder to the exterior, conveying urine 

 and semen in the male sex. urine only in the female: in some birds a penial 

 groove for the conveyance of semen only. The urethra in the male is always 

 a part of the penis, or penial urethra, continuous usually with the urethral part 



