Rodent External Features

Question 1

3 divisions of rodent classifications

Answer 1

Myomorphs
Hystricomorphs
Sciuromorphs

Question 2

What are myomorphs?

Answer 2

Mouse-like rodents. Also includes gerbils and hamsters.

Question 3

What are hystricomorphs

Answer 3

Porcupine-like rodents. Includes giant capybara, Guinea pigs and chinchillas.

Question 4

What are sciuromorphs?

Answer 4

Squirrel-like rodents. Includes beavers and chipmunks.

Question 5

How many teeth do myomorphs generally have? What tooth types are these divided into?

Answer 5

16 = 4 open-rooted (aradicular) incisors, no premolars, 12 closed-rooted (brachydont) molars.

Question 6

Comment on myomorphs genitalia.
Comment on myomorphs gestation and young.

Answer 6

Separate anal, genital and urinary openings in females. Anogenital distance useful for sexing.
Short gestation and altricial (helpless) young.

Question 7

How many teeth do hystricomorphs generally have?
How are these divided into tooth-types?
Why do they generally have more dental issues than myomorphs?

Answer 7

20 = 4 incisors, 4 premolars, 12 open-rooted (aradicular) molars.
Open-rooted so dental disease more likely.

Question 8

Comment on hystricomorphs genitalia.
Comment on hystricomorphs gestation and young.

Answer 8

Separate anal, genital and urinary openings in females. Anogenital distance not always useful for sexing.
Long gestation and precocial young.

Question 9

Rat head shape and neck length.
What colour are rats teeth pigmented?
Why?

Answer 9

Pointed and triangular heads and short necks.
Pigmented yellow-orange.
Store iron in teeth.

Question 10

What is porphyria?

Answer 10

When the harderian gland overproduces porphyrin pigment and this make the tears and nasal secretions dark red in colour.

Question 11

What is the philtrum?
What do the vibrissae do?

Answer 11

Cleft upper lip.
The vibrissae (whiskers) are highly developed to sense touch.

Question 12

Describe hystricomorph necks.
Colour of hystricomorph teeth.
What anatomical feature separates the rostral and caudal parts of the oral cavity?
Name the sulcus in the roof of the mouth of the Guinea pig.

Answer 12

Short and thick necks.
White teeth.
Cheek folds.
Labionasal sulcus

Question 13

How many digits on myomorphs forefoot?
How many digits on myomorphs hindfoot?
Name the pads in the feet from proximal to distal. (FL and HL)

Answer 13

4 digits on forefoot digit 1 (medial) is very reduced.
5 digits on the hindfoot.
Carpal —> metacarpal —> digital
Tarsal —> metatarsal —> digital

Question 14

How many digits on the forefoot of hystricomorphs?
How many digits on the hindfoot of hystricomorphs?
Name the 2 pad types on the forefoot.
Name the 2 pad types on the hindfoot.

Answer 14

4 on forefoot (digit 1 missing)
3 on hindfoot ( digits 1 and 5 missing)
Carpal and palmar pads on fore.
Tarsal and plantar pads on hind.

Question 15

What is a common presenting complaint seen in rats’ mammaries?
How many pairs of nipples in myomorphs?

Answer 15

Tumours
6 pairs of nipples

Question 16

How many pairs of nipples in Guinea pigs and in what region?
How many pairs of nipples in the chinchillas? In what regions

Answer 16

1 pair in the inhumanly region.
3 pairs (2 thoracic and 1 inguinal)

Question 17

What anatomical feature give rodents an a cute sense of hearing?
What dental problem do hystricomorphs often present with and why?
What rodents have clavicles?
What stance do rodents have on their hind limbs?
What stance do most rodents have on forelimbs?
I’m which rodents do the pelvic bones separate at parturition?

Answer 17

Very large tympanic bullae.
Dental overgrowth because teeth are aradicular (open-rooted) and constantly growing.
Rats, Guinea pigs and chinchillas have clavicles.
Plantigrade stance on hind limbs.
Most have digits grade stance on forelimbs.
Pelvic bones separate in mice and Guinea pigs.

Question 18

What type of connective tissue is the rodent mandibular symphysis made of? What does this allow for?
What 2 features of the rodent skull are prominent?

Answer 18

Cartilage — allows for mobile chewing actions.
Zygomatic arch and tympanic bulla.