Vance Lenin B. de Leon Bio 102 Lab (Dayao)

Marianne Frances P. Montiel July 22, 2013

Worksheet No. 2

1. What are the 3 components of the skull and give their significance.

The skull consists of three embryonic components: the chondorcranium,

part of the endoskeleton that forms around the brain and organs of

special sens; the splanchnocranium, originally forming in the pharyngeal

region as endoskeletal gill supports; and the dermatocranium, consisting

of membrane bones that, in the majority of vertebrates, superficially invest

the endoskeletal portions of the skull.

2. How many occipital condyles does the skull of the ff have: dogfish, turtle,

chicken and cat?

Dogfish - 2

Turtle - 1

Chicken - 1

Cat - 2

3. What is the function of the occipital condyle?

Smooth, rounded knobs on each side of the foramen magnum, where the

skull articulates with the first vertebra. Mammals have two occipital

condyles, birds and reptiles have only one.

The function of the occipital condyles on the skull is to make a surface for

articulating with the first cervical vertebra the first bone of the neck.

4. Identify the type of jaw suspension of the ff organism: dogfish, turtle, chicken

and cat.

Dogfish - Orbitostylic

Turtle – Modified hyostylic

Chicken - Autostylic

Cat - Craniostylic

5. What are dermal bones?

A dermal bone or membrane bone is a bony structure derived

from intramembranous ossification forming components of

the vertebrate skeleton including

the skull, jaws, gills, fins andexoskeleton (of tortoises and turtles). In contrast

to endochondral bone, dermal bone does not form from cartilage that

then calcifies. Dermal bone is formed within the dermis and grows by

accretion only – the outer portion of the bone is deposited by osteoblasts.

The function of some dermal bone is conserved throughout vertebrates,

although there is variation in shape and in the number of bones in the skull

roof and postcranial structures. In bony fish, dermal bone is found in the

fin rays and scales. Special examples of dermal bones include

the clavicle, patella, and os cordis.

6. What are cartilage bones?

It is deposited where the hyaline cartilage already exists. In the process,

the existing cartilage undergoes degenerative changes and disappears.

The processes of endochondral and intramembranous ossification are the

same in that of both consist empregnation of collagenous matrix with

hydroxyapatite crystals. The difference is that in endochondral ossification,

cartilage must be removed before bone can be deposited. In both cases,

the immediate result is formation of temporary spongy bone. The latter, in

turn, is eroded and replaced by compact, spongy bone, or a marrow

cavity, depending on its location.

7. List examples of dermal bones in the skull.

Premaxillae, maxillae, roofing bones (i.e. intertemporal, supratemporal,

tabular, squamosal and quadratojugal)

8. List examples of cartilage bones in the skull.

Ethmooid plate, palatoquadrate, Meckel’s cartilages, nasal capsule, otic

capsule and hyoid arch component

9. What is the function of the splanchnocranium of the dogfish.

It supports the gills and furnishes attachment for the respiratory muscles.

10. How many gill arches are there in the dogfish?

There are 7 gill arches in the dogfishes.

11. Differentiate the different gill arches and give the function.

The first arch, mandibular arch, is the largest and most modified of the

series. It is composed of dorsal and ventral halves. Each side of the halves

is called the palatoquadrate or pterygoquadrate cartilage. It sends up a

well-developed orbital process into the orbit. The palatoquadrate bears

the teeth and constitute the upper jaw of the animal. The ventral half of

the mandibular consists of two halves known as Meckel’s cartilages.

The hyoid arch is the second which is more slender than the mandibular

arch, to the posterior face of which it is closely applied. It consists of a

ventral median piece, the basuhyal; a slender bar, the ceratohyal, on

each side of the basihyal; and a stout piece, the hyomandibular, dorsal to

each ceratohyal.

The remaining arches, known simply as gill or branchial arches, are similar

to each other. Each type consists of five pieces, named from the dorsal

side ventrally: pharyngobranchial, the most dorsal piece, elongated and

directed posteriorly; epibranchial, the succeeding, much shorter piece;

ceratobranchial, another elongated piece; hypobranchial, curved

ventral pieces, of which there are but three pairs to the five branchial

arches; and the two basibranchials that are small one situated between

the medial ends of the first and second pairs of hypobranchials and a

large posterior piece between the bases of the fifth ceratobranchials

terminating in a caudally directed point.

12. What are some unique features of the mammalian skull? List 5.

The mammalian skull is completely ossified except for a small part of the

ethmoid region. The number of bones in the mammalian skull is greatly

reduced, as compared wih the number in primitive tetrapods, partly

though the loss of dermal bones and partly through extensive fusions,

especially among the loss of dermal bones and partly through extensive

fusions, especially among the cartilage bones. Other characteristic

features include the completely enclosed and greatly expanded cranial

region containing the brain; paired occipital condyles; the formation of a

secondary palate, causing the internal nares to open behind the mouth

cavity, and a diphyodont and markedly heterodont dentition, related to

mastification of food; the greatly enlarged temporal fenestra formed by

the reduction of the temporal roof and loss of the postorbital bar as the

teomporalis muscle was differentiated; etc.

13. Differentiate anapsid, diapsid and synapsid. Give example organisms.

(Make use of our specimens if applicable.)

Anapsid - A reptile having a skull with no temporal openings. Anapsids

probably gave rise to the diapsids and synapsids.

- Turtles

Diapsid - Are a group of tetrapods that developed two holes (temporal

fenestra) in each side of their skulls, about 300 million years agoduring the

late Carboniferous period.

- Crocodiles

- Lizards

- Snakes

- Tuataras

- Birds

Synapsid - synonymous with theropsids, are a group of animals that

includes mammals and every animal more closely related to mammals

than to other living amniotes. They are easily separated from other

amniotes by having a temporal fenestra, an opening low in the skull

roof behind each eye, leaving a bony arch beneath each; this accounts

for their name.

- Pelycosaurs

- Therapsids

- Mammal-like Reptiles

- Moose

- Black Bear