[Illustration: FIG. 3.--Muscular System and Vascular System (part) of Xenopus and Rana.] 2. Make an incision in the body wall, slightly to the right side of the abdominal vein, which may now be seen clearly on the inner side of the body wall. Carefully detach this vein from the abdominal wall. _Second Day._ =Skeletal System= (_Part_). 1. Remove the pectoralis muscles covering the body between the arms to show the bones of the central part of the shoulder girdle and sternum, viz.:-- (_a_) The thick coracoids. (_b_) The more slender clavicles anterior to them, both extending from the base of the arm on each side towards the centre of the body. (_c_) The sternum, consisting of a median row of cartilages which are believed to be derived from the shoulder girdle. It does not, therefore, correspond to, or is not homologous with, the sternum of the Pigeon or the Rabbit, which is derived from the ribs. The sternum consists of the following parts: (i) The two epicoracoids consisting of cartilage. (ii) The metasternum which is broad and consists of cartilage only. [Illustration: FIG. 4.--Pectoral Girdle of Xenopus and Rana.] [In the Frog the sternum is composed of the following parts:-- (_i_) _The omosternum consisting of two parts, an anterior cartilaginous part (sometimes called the omosternum) and a posterior bony part (sometimes called the episternum)._ (_ii_) _The two epicoracoids consisting of cartilage._ (_iii_) _The metasternum consisting of two parts, an anterior bony part (sometimes called the sternum) and a posterior cartilaginous part (sometimes called the xiphisternum)._] Make a sketch of the pectoral girdle. 2. Cut through the coracoids and clavicles on each side, close to the base of the arm, and carefully remove this part of the pectoral girdle and sternum so as to show the heart lying underneath. [Illustration: FIG. 5.--Dissection of Xenopus and Rana to show the Alimentary System, etc.] Alimentary System. Make a sketch showing:--The heart, lungs, liver, gall bladder and bile duct going to the duodenum, exposed parts of the stomach, duodenum, small intestine (or ileum), large intestine, urinary bladder, pancreas, and spleen. Third Day. =Vascular System= (_continued_). A. Venous System. 1. Note:-- (_a_) The heart lying in the thin pericardium, the two auricles, the single ventricle, the truncus arteriosus which divides into two branches. Remove the pericardium from the heart, and tilt the apex of the heart forwards, noting the sinus venosus into which the right and the left superior venæ cavæ (or precavals) and the single inferior vena cava (or postcaval) open. (_b_) The veins passing from each side of the sinus venosus. Each superior vena cava is joined by the following branches:--