First set of review questions for the third exam   You are responsible for explaining all the photographs and diagrams on the web pages corresponding to this section of the course.   You should know what subdivision of which germ layer each of the following develops from. For example the lens develops from somatic ectoderm, more specifically from a placode. Adult kidney answer Brain answer Capillaries, veins, arteries answer Cochlea answer Epidermis answer Facial Skeleton answer Feathers answer Fish scales answer Hair answer Heart answer Intestine answer Liver answer Lungs answer Motor nerves answer Olfactory nerves answer Otoliths answer Pancreas answer Pigmented retina answer Pituitary gland answer Postganglionic autonomic nerves answer Reptile scales answer Salivary glands answer Schwann cells answer Semi-circular canals answer Sensory nerves (including in skin) answer Sensory retina answer Skeletal muscles answer Skeleton in the rest of the body answer Spinal cord answer Stomach answer Thyroid gland answer   Pairs of somites develop along both sides of what mesodermal organ? Along what ectodermal part? neural tube Each somite subdivides into what three parts? (one whose cells differentiate as skeletal muscle, another forms skeleton, and the third forms the inner-leathery layer of the skin). Which of these three subdivisions then subdivides into an anterior and a posterior part? Each anterior part then fuses with the posterior part of what, so as to form what anatomical structure? Somite cells all disperse, and later in development you can only see remnants of where they had been: Can you suggest functional or mechanical reasons why the vertebrate body is segmented by transient rather than permanent blocks if cells? Maybe segmentation has a physical cause] In fact, why use aggregated blocks of cells at all? People hypothesize that wave-like gradients of diffusing chemicals are what control where the somites are formed; so why not have those chemical gradients directly determine which cells will differentiate into muscle, bone and dermis. (Why not eliminate the middleman?) TO BE CONTINUED       back to syllabus